diff --git a/src/index.js b/src/index.js
index d3df487..bd63dbb 100644
--- a/src/index.js
+++ b/src/index.js
@@ -7,31 +7,38 @@ const getPort = require('get-port');
 const pify = require('pify');
 const createCert = require('create-cert');
 
-const createTestServer = opts => Promise.all([
-	getPort(),
-	getPort(),
-	createCert(opts && opts.certificate)
-])
-	.then(results => {
-		const port = results[0];
-		const sslPort = results[1];
-		const cert = results[2];
-
+const createTestServer = opts => createCert(opts && opts.certificate)
+	.then(cert => {
 		const app = express();
 		app.caCert = cert.caKeys.cert;
-		app.url = `http://localhost:${port}`;
-		app.sslUrl = `https://localhost:${sslPort}`;
+		Object.defineProperty(app, 'url', {
+			get: () => typeof app.port === 'undefined' ? undefined : `http://localhost:${app.port}`
+		});
+		Object.defineProperty(app, 'sslUrl', {
+			get: () => typeof app.sslPort === 'undefined' ? undefined : `https://localhost:${app.sslPort}`
+		});
 
 		const server = http.createServer(app);
 		const sslServer = https.createServer(cert.keys, app);
 
 		app.listen = () => Promise.all([
-			pify(server.listen.bind(server))(port),
-			pify(sslServer.listen.bind(sslServer))(sslPort)
+			getPort().then(port => {
+				app.port = port;
+				return pify(server.listen.bind(server))(port);
+			}),
+			getPort().then(sslPort => {
+				app.sslPort = sslPort;
+				return pify(sslServer.listen.bind(sslServer))(sslPort);
+			})
 		]);
+
 		app.close = () => Promise.all([
-			pify(server.close.bind(server))(),
-			pify(sslServer.close.bind(sslServer))()
+			pify(server.close.bind(server))().then(() => {
+				app.port = undefined;
+			}),
+			pify(sslServer.close.bind(sslServer))().then(() => {
+				app.sslPort = undefined;
+			})
 		]);
 
 		return app.listen().then(() => app);